Psychiatric patient killer awaits sentence

A NSW man who fatally stabbed a fellow psychiatric patient in the neck says if he wasn't diagnosed with schizophrenia, hospitalised and medicated, both he and his victim "would still have our freedom and our lives".

Thomas Dillan Stone, 27, pleaded guilty in late 2018 to murdering Robert James Mitchell on the grounds of Morisset Hospital, in Lake Macquarie, in February 2017.

Stone stabbed the 41-year-old three times with a kitchen knife in the low-security cottage they shared, court documents state.

The victim was heard by two other patients yelling "Stop, stop, Tom, Tom" and seen covered in blood before staggering along a footpath towards another building.

Mr Mitchell was treated by medical staff but died at the scene.

In a triple-zero phone call played at his NSW Supreme Court sentence hearing on Friday, Stone is heard telling the operator he "chucked" the weapon in a lake and his victim - "just another patient" - had left to get help.

"Does he need an ambulance?" the female operator asks, to which Stone replies: "Probably."

Mr Mitchell's mother, Gay Crooks, told the court she is haunted by the thought of her son's final moments and traumatised by the sight of him in the morgue.

"Knowing the fact that my son, Rob, had desperately made every effort to get to safety and to get help for himself," she said, reading from her victim impact statement.

"The distance, the pathway ... with such life-threatening injuries. This truly causes me the most heartbreaking pain."

An undated, handwritten letter of Stone's was also tendered in court on Friday.

"At the end of the day I can't change what happened, but I wish things were different," it reads.

"I know what I did was wrong and I sincerely apologise to Rob's friends and family and to the nurses who treated him and anyone else affected by my wrong actions."

The 27-year-old writes that he strongly believes if he wasn't "wrongfully" diagnosed with schizophrenia, made a forensic patient, hospitalised and prescribed Paliperidone - an antipsychotic medication - "then me and Mr Mitchell would still have our freedom and our lives".

A crown witness, forensic psychiatrist Dr Jonathon Adams, said there was clear evidence Stone "transitioned down the levels of security" at the hospital.

At the time of the murder, Stone cooked his own meals, attended groups and meetings, and was granted unsupervised leave from the hospital campus.

"My view ... is that I do not elicit any clear evidence to conclude there was a nexus between Mr Stone's symptoms of schizophrenia and the offence," Dr Adams said.

The psychiatrist said he believed Stone would "manifest a significant violence risk" for a number of years.